import { test, expect } from "bun:test";
import { resample } from "../../src/dsp/resample.ts";

// Reference: the direct windowed-sinc evaluation (the original implementation), used to check the cached path is exact.
function reference(x: Float32Array, from: number, to: number): Float32Array {
  const sinc = (v: number) => (v === 0 ? 1 : Math.sin(Math.PI * v) / (Math.PI * v));
  const ratio = to / from, outLen = Math.round(x.length * ratio), out = new Float32Array(outLen);
  const cutoff = Math.min(1, ratio), half = 16 / cutoff;
  for (let j = 0; j < outLen; j++) {
    const t = j / ratio;
    const lo = Math.max(0, Math.ceil(t - half)), hi = Math.min(x.length - 1, Math.floor(t + half));
    let acc = 0, wsum = 0;
    for (let i = lo; i <= hi; i++) {
      const d = i - t;
      const w = 0.42 + 0.5 * Math.cos((Math.PI * d) / half) + 0.08 * Math.cos((2 * Math.PI * d) / half);
      const k = cutoff * sinc(cutoff * d) * w;
      acc += x[i]! * k; wsum += k;
    }
    out[j] = wsum !== 0 ? acc / wsum : 0;
  }
  return out;
}

const noise = (n: number) => { let s = 1; return Float32Array.from({ length: n }, () => ((s = (s * 16807) % 2147483647) / 2147483647) * 2 - 1); };

test("2:1 decimation is bit-identical to the direct evaluation and much faster", () => {
  const x = noise(44100);
  expect(Array.from(resample(x, 44100, 22050))).toEqual(Array.from(reference(x, 44100, 22050)));
  const big = noise(44100 * 10);
  const time = (f: () => unknown) => { const t0 = performance.now(); f(); return performance.now() - t0; };
  time(() => resample(big, 44100, 22050)); // warm-up (JIT)
  const fast = time(() => resample(big, 44100, 22050)), slow = time(() => reference(big, 44100, 22050));
  // measured ~40x; a 4x margin keeps this robust on a loaded machine
  expect(fast * 4).toBeLessThan(slow);
});

test("non-integer ratios are unchanged", () => {
  const x = noise(4800);
  expect(Array.from(resample(x, 48000, 44100))).toEqual(Array.from(reference(x, 48000, 44100)));
  expect(Array.from(resample(x, 22050, 44100))).toEqual(Array.from(reference(x, 22050, 44100)));
});